Plastic materials are used in a wide variety of applications on account of their advantages including light weight and ease of working. Because of their drawback of poor mar resistance on the surface, improvements were made in the prior art in order to provide surface protection to substrates.
When substrates of plastics and light metal materials having soft surfaces are used in the application where a high level of mar resistance is required, siloxane-based thermosetting hard coat compositions are used. For the siloxane-based hard coat compositions, a number of technical proposals were made. For example, JP-A S51-2736 and JP-A S55-94971 disclose coating compositions comprising a partial condensate of trihydroxysilane and colloidal silica. JP-A S48-26822 and JP-A S51-33128 disclose coating compositions comprising primarily a partial condensate of alkyltrialkoxysilane and tetraalkoxysilane. These compositions are still not fully satisfactory in mar resistance and coating liquid stability.
JP-A H11-286652 and JP-A H10-324827 intend to promote curing of coating compositions by adding thereto a titanium chelate compound or a partial hydrolytic condensate thereof so as to play the role of a catalyst for promoting cure. Although these proposals achieve some improvements, problems of stability and crack resistance are left unsolved.
In the inorganic siloxane structure based curable coating compositions which have been proposed thus far, siloxane linkage is sensitive to humidity with time because of high water vapor permeability. There exists a need for a hard coat composition which obviates the problem of crack generation by external shocks over a period of time and has improved mar resistance.